Depth of Field Scale
© Wendy Folse
Part I:
Ever wonder what all those little numbers on the front of your lens means? Why are they there and what do you do with them? Thanks to the new modern autofocus slrs, these numbers are fast disappearing. Many people never even give them a second thought and consider them as mere decorations. What a shame.
Those numbers used to be considered an invaluable part of the photographer's toolbox and learning to use an slr always started with learning the secret code of the numbers. It has been said that the reason so many people were put off by slrs in the past was because they were too confusing. When people see the jumble of numbers running around the barrel, they tend to panic. No need. It really is just a calculator of sorts. Actually, it is a calculator without the lcd readout. Most of the new auto everything cameras still use the calculations internally so that the user isn't even aware of them. Why should we bother when the camera can do it all for us? Well, maybe because this scale is the key to your creative interpretation of the scene, instead of a preprogrammed algorithm that locks you into a certain formula.
Learning to control the depth of field is a creative tool that will enable you to use an slr the way it was intended. To control the light creatively, to render a photograph of the scene as you interpret it, other wise if we just wanted perfect pictures we could buy postcards. The reason that these little numbers are so important to a photographer is precisely because photographers do not want to constantly be doing mathematical equations. Think of them as a photographer's slide rule.
If you are still scratching your head thinking, no way this is too confusing, just bare with us. We promise that it is easier than you think and you don't even have to do the math because the manufacturers have done it all for you. They even went to all the trouble to engrave a handy dandy calculator right on the lens for you. Now wasn't that nice of them.
Take out your camera and your favorite lens. Look at the barrel of the lens. The lens used in the following graphic is a normal 50mm lens and may look different from yours. It doesn't matter because the principles are the same. Each depth of field scale is calculated for the particular lens so the scale on your lens will calculate the distance and depth of field based on the characteristics of that lens. The lens maker has done the math for you and engraved the results right on the barrel.
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